In many sensing applications it is desirable to ascertain the capacitance or capacitance change in a capacitor formed by two conductive plates in which a dielectric material is moved in the spacing between the plates. In one example, a capacitor is formed by two spaced plates with paper or other dielectric being moved along a path between the plates, where detecting changes in the capacitor value can indicate the presence or absence of a sheet of paper between the plates. One example includes a first plate that forms an external surface which is connected to a device ground and the other plate is an active element that is either an integral part of the device or is permanently connected to the device by wire or cable. The two plates are separated by a fixed distance, and material is passed between the plates. Of interest are minute changes in sensor capacitance due to insertion of material rather than the absolute overall value of the capacitance with no intervening material. Other sensing situations occur in which it is desired to detect changes in an inductance of a structure or fluid. Previously, sensing systems for detecting capacitance or inductance changes employed various analog components or subsystems, or banks of switched capacitors to comparing voltages or generating pulses of certain duration when the sensed capacitor or inductor is energized. However, conventional reactance sensing systems suffered from limited dynamic range and/or from limited resolution.